Chlorine is used in many everyday products. For example, it is used in producing safe drinking water, in the production of paper products, in textile production, in petroleum products and chemicals, medicines, antiseptics, insecticides, foodstuffs, solvents and cleaners, paints, plastics, refrigerant fluids, chloromethane, ethylene glycol, chloroform, carbon tetrachloride and many other products.
In its elemental form, chlorine is a greenish yellow gas, which combines directly with many elements. Chlorine can be produced in a number of ways. One of the largest is through the electrolysis of a sodium chloride (common table salt) solution, often called “brine.” As brine, the sodium chloride has dissociated into sodium cations and chlorine anions. During the electrolysis process, the chloride ions are oxidized at the anode to form chlorine gas and water molecules are reduced at the cathode to form hydroxyl anions and hydrogen gas. The sodium ions in the solution and the hydroxyl ions produced at the cathode constitute the components of sodium hydroxide formed during the electrolysis of sodium chloride.
The chlorine and hydrogen produced in the electrolysis process undergo further processing in the form of chlorine liquefaction, hydrochloric acid production or hypochlorite production. A chlorine liquefaction system consists of four sections namely, chlorine drying, chlorine compression, chlorine liquefaction, and liquid chlorine storage. Chlorine drying can be carried out in a multi-stage operation in which sulphuric acid is used to “dry” (i.e., remove water) the chlorine gas. From the drying system, the chlorine gas is piped to a chlorine gas compressor. In the chlorine gas compressor, the pressure of the chlorine gas is increased to a level suitable for a chlorine liquefaction unit. The chlorine liquefaction unit includes one or more heat exchangers in which the chlorine gas is cooled and condenses to a liquid. Cooling is typically performed by a closed-loop compressor based refrigeration system.
Normally the chlorine and the heat transfer fluid used to liquefy the chlorine are substantially isolated from each other. A problem of particular concern in chlorine liquefaction plants, however, is one of safety in the event the chlorine and the heat transfer fluid used to liquefy the chlorine come into mutual contact. When such mutual contact does occur, it is usually, but not necessarily, due to failure of the condenser through which both materials flow. The failure can range from inconsequential, as for example where a very small leak and little or no reaction have occurred, to catastrophic, as for example where there is a major rupture of one or more tubes within the condenser. Between these extremes important adverse consequences can occur, as for example unacceptable contamination of the chlorine by heat transfer fluid or vice versa, with or without contamination by reaction products.